Bus transfer system



Nov. 16, 1948. I N N 2,454,117

BUS TRANSFER SYSTEM Filed Feb. 28, 1947 ZSheets-Slieet 2 72a .4 W q m ATTORNEY Patented Nov. 16, 1948 BUS TRANSFER SYSTEM Earl B.

Westinghouse burgh, Pa., a. corpora Ankenman, Braintree,

Electric Corporation,

Mass, assignor to East Pittstion of Pennsylvania Application February 28, 1947, Serial No. 731,510 9 Claims. (Cl. 318-393) My invention relates to bus transfer systems direct-current motors. In such systems, the motor to be accelerated to the desired operating speed is first energized from starting connections whose voltage is gradually raised to the value required for the desired motor speed, and the accelerated motor is then transferred to the running connections to which the motor remains attached during its further performance. Systems of this kind are in use for sectional fabricating machinery, such as sectional paper machines, which have several motors operated from a variable-voltage generator and whose sections must permit being started independently of other sections that may be running at the time of the start.

The known bus transfer systems of the kind mentioned are controlled by an electromagnetic voltage-responsive relay whose contacts initiate the switching operation when the voltage difference between the running bus and the starting bus becomes sufficiently low. The transfer performance of such a voltage relay is sometimes unsatisfactory or rough because the electromagnetic relay may change its pick-up point due to changes in temperature, and it may happen that the motor, though under the proper voltage, has as yet not sufliciently accelerated for a smooth transfer.

It is an object of my invention to provide bus transfer systems that secure automatically a smooth transfer at any time. More in particular, my invention aims at devising a transfer system whose transfer conditions are not affected by those changes in temperature or other ambient conditions that are apt to disturb the proper performance of the electromagnetic voltage relays heretofore used for initiating the switching operation. Another more specific object of my invention is to permit and initiate a bus transfer only when the voltage differential between starting and running buses is sufficiently low or zero and when, in addition, the motor has ceased accelerating;

These and other objects of the invention as well as the means provided by the invention for for variable-voltage achieving them will be apparent from the following description of .the embodiments illustrated in the drawings, in which:

Figure 1 represents the circuit diagram of a sectional drive appertaining to a paper machine and designed in accordance with the invention, while Fig. 2 is a similar circuit diagram of another embodiment also representing a sectional paper machine drive.

According to Fig. 1, the machinery to be driven comprises a number of sections, such as those denoted by SI and S2, with appertaining directcurrent motors MI and M2 which can be started and operated independently of each other and independently of any other sectional drive but which during their operation must maintain a given speed or positional relation to one another. As illustrated, the machine section SI consists of a roll press from which the material I passes over guide rollers 2, 3 and 4 through the section S2, here represented as a calender.

The armature 5 of drive motor MI has one of its poles permanently connected to a common negative bus 8 of a running generator GR. and a starting generator GS. The other pole of the motor armature 6 is selectively connectible to the positive bus I of the starting generator GS and to the positive bus 8 of the running generator GR. The selective connection is effected by means of two'mutually interlocked contactors CI and C2 under control by two electromagnetic relays RI and R2 in conjunction with an electronic tube circuit and other circuit devices to be described in a later place. The contactors CI, C2 and the appertaining other control devices represent together a control system which is denoted as a whole by CSI.

The field winding 9 of drive motor MI is connected to a suitable source III of constant directcurrent voltage through a rheostat II. The armature I2 of the drive motor M2 has its negative pole connected to the common generator bus 6 while its positive pole is connected to the starting bus I or the running bus 8 under control by a control system CS2 which contains contactors and relays designed and operative in the same manner as those of the control systems CSI and hence not illustrated in detail. The field winding I3 of motor M2 is energized from a constant voltage source I4 through an adjusting rheostat I5. While the voltage sources I0 and I4 are schematically represented as separate units, they may, oi course, consist of one and the same device which may be identical with the direct-current source described hereinafter as supplying energization for the direct-current elements of the control system CS I.

The contactor C2 has a contact I! which, when closed, connects the motor MI to the running bus 8, The contact member I1 is controlled by a coil I8 which actuates also an interlock contact I9. The contactor CI has a main contact 2I which, when closed, connects the motor MI to a voltage source ti 3 the starting bus l. The control coil 22 of contactor Cl actuates also an interlock contact 28 in the coil circuit of contactor (C2. The inter= lock contact it of contactor C2 is series connected in the circuit of coil 22. Due to these interlock connections, only one or contactors Cl and C2 can be closed at a time. The motor circuit controlled by contact 2i includes a series rh'eostat it so that the voltage drop across this rldeostat is a measure of the current drawn by the motor armature 5 when the motor Ml is ener= gized from the starting bus l.

The excitation for the contactor coils l8 and 22 is derived from the terminals 25 and 2S oi? a direct-current source which, as mentioned above, may be identical with the source or held excitation for motors Mi and M2. The coil circuit of contactor C2 includes in series a normally open contact 21 of a control relay R8, while the coil circuit of contactor Cl includes in series a normally closed contact 28 of the same relay Rt.

Both contacts 2? and 28 are under control by the relay coil 29. The circuit of contactor coil 22 extends further through a control contact 30 to be actuated by the operator for starting the motor Mi.

The relay coil 29 receives excitation from the terminals 25 and 26 under control by an electronic discharge tube 3|, for instance, of the thyratron type. The plate circuit of this tube, extending through the coil 29, includes also a control contact 3 appertaining to a voltage relay R2 whose control coil 33 actuates also two additional contacts 34 and 35.

The tube 3| serves a trigger device. Its control grid 36 is connected through a resistor 37 and the above-mentioned contact 34 to the tap point Pi of the current measuring rheostat 24 in the starting connections of the motor Ml. A grid bias capacitor is denoted by 38. Connected between the starting bus 1 and the running bus 8 is a rheostat 39 which develops a voltage drop corresponding to the voltage difierence between the running bus 8 and the starting bus 7. This connection is controlled by the above-mentioned contact 35 of the voltage relay R2 whose coil 33 is also connected across the buses '1 and 8. The grid circuit of tube 3| 36 through resistor 31, contact 34, point Pl of rheostat 24, point P2, rheostat 39, point P3, and contact 40 to the cathode of tube 3|. It will be noted that this grid circuit contains two sources of control voltage, one being represented by the tapped portion Pl-PZ of rheostat 24 and the other by the tapped'portion P2-P3 of the rheostat 39. The voltage imposed on the grid circuit along the rheostat portion Pl-P2 is proportional to the current of the motor Ml, while the voltage imposed on the grid circuit along the rheostat portion P2 P3 is proportional to the voltage differential between the starting and running buses 1 and 8. This grid circuit, however, is closed only when the voltage relay R2 is in the illustrated dropped-on condition and when the contactor Cl is energized to attach the motor Ml to the starting connections.

The armatures of the generators GR and GS are denoted by 46 and d2, respectively. The field winding 33 of the running generator is excited from a source a l of constant voltage through a controlling rheostat to. The field winding 42-6 of the starting generator GS receives excitation from through a control rheostat Gt. The voltage sources at and ll, here separately illustrated, may be associated with the abovecan be traced from grid 1 mentioned other sources of direct-current voltage.

The rhecstats ii and B5 in the motor field circuits, once properly adjusted, need not as a rule be actuated during the normal performance of the system. Consequently, the speed of the motors Ml and M2 is normally determined by the voltage of the running generator GR or of the starting generator GS, and these voltages are adjustable by the respective rheostats t5 and 58. The rheostat Q5 of the running generator GR is normally maintained at a setting which corresponds to the desired operating speed of the sectional fabricating machinery. The coil circuit of the voltage relay R2 is so rated that the relay R2 picks up when the voltage of the starting generator GS is below a given value which is lower than the voltage of the running generator GR within the normal voltage or speed range of the system. The tube 3! has its circuits so rated that a triggerefiect occurs when the voltages of the starting bus '1 and running bus 8 are nearly equal, but the triggering is also dependent upon the disappearance of accelerating current in the motor circuit as will be understood from the description of an operating performance following presently.

For the purpose of explanation, it is assumed that the motor M2 and, possibly other motors of the sectional machinery, are attached to the running connections, 1. e., between buses 8 and 8, and hence operate at the proper speed as determined by the setting of the rheostat 45. The motor MI is assumed to be at rest and in condb tion to be started. For starting, the operator closes the contact 30. This completes the circuit of coil 22. Contactor Cl picks up and connects the motor armature 5 at contact 2| to the starting bus 1. The operator now starts the generator GS or if the generator was running, applies an increased field excitation thereto by progressively adjusting the rheostat 48. At the moment when contact 30 is closed, the full running voltage is eflective across buses 1 and 8. Consequently, the voltage relay R2 picks up, opens the plate circuit of tube 3|, and interrupts the appertaining grid circuit. As the starting voltage increases and causes the motor Ml to accelerate, a point will be reached where the voltage drop between buses l and 8 becomes insufficient to energize the coil 33 for a continued opening of the relay R2. As a result, the relay R2 drops out and prepares the tube circuits for the subsequent triggering and switching performance. As soon as this occurs, two cumulative blocking voltages are imposed on the grid circuit. These two voltages, as explained above, correspond to the declining voltage differential between buses I and 8 and to the declining current flowing through the starting connections of-motor M l. Thereafter, as soon as the voltage diherential between buses 1 and 8 become zero or drops below a given small value, the blocking voltage between points P2 and P3 of rheostat 39 disappears. This causes the tube 3! to be trlggered unless at that moment the motor M i is still accelerating. The accelerating current, causing a corresponding voltage drop between points Pi and P2 of rheostat 2d, maintains the tube' under cut-ofi bias. but when the motor Ml has reached the proper speed, this cut-on bias is also eliminated and the tube will then start conducting. As a result, coil 29 of relay RH becomes energized and interrupts the coil circuit of contactor Cl, while closing the contact "ll of the coil circuit of contactoz- C2. Contractor C l interrupts the starting connections, and contactor C2 establishes the permanent running connections for motor MI. The starting generator GS can then be stopped or its voltage can be reduced to zero,

so that this generator is thereafter available for starting other machine sections. Motor. MI will continue running at the speed determined by the selected field excitation of generator GR until the current supplied from this generator ceases or until contactor PC is opened by the operator or by protective control devices.

It will be recognized from the foregoing that the bus transfer is controlled by the tube 3| and hence is virtually not affected by changes in ambient temperature or other conditions. This transfer is further jointly dependent on the simultaneous existence of two conditions, namely, the disappearance or given decrease in the voltage diflerential between starting and running buses and on the disappearance or given decrease of accelerating current in the motor to be started. Thus. a smooth transfer is secured under any condition of operation. To be sure, the voltage point of response of the relay R2 may be sub- Jected to the same changes that occur in the electromagnetic control relay of the known transfer systems. However, in the above-described embodiment of my invention, the relay R2 does not control the bus transfer but serves merely as an auxiliary device which secures an increased life of the electronic device by switching the latter into the circuit only when the operating conditions of the system are close to a status where the more accurate control effect of the tube circuit is to be utilized. In other words, the rating of the coil circuit in relay R2 is such that the dropout voltage is always below the voltage range in which tube is to be efiective. Hence a change in the relay calibration does not affect the control performance proper. It should also be understood that if desired, the relay'R2 can be eliminated or that it may be replaced by another electronic discharge device, for instance, in the manner shown in the embodiment of Fig. 2 and described hereinafter.

According to Fig. 2, a fabricating machinery with independently operable sections S3 and S4 is driven by respective motors M3 and M4 which are energized from the common negative bus 6, the starting bus I and the running bus 8 of a variable voltage system energized from a starting generator GS and a running generator GR in the same manner as described more in detail above with reference to Fig. 1.

The bus transfer performance for motor M3 in Fig. 2 is controlled by a control system CS3, and the corresponding bus transfer for motor M4 is under control by a. similar system CSl, the latter not being shown in detail.

The control system CS3 includes two mutually interlocked contactors C3 and C4. The main contact 5| in contactor C3 is controlled by a coil 52, together with an interlock contact 53, and serves to connect the motor M3 across the buses B and in series with a current measuring rheostat 5L The main contact 55 of contactor C4 is controlled by a coil 56 which actuates also four additional contacts denoted by 51, 58, 59 and 60, respectively.

A rheostat 6| is connected across the starting and running buses and 8 and has a tap point P4 connected to the grid 52 of an electronic tube 53. The grid circuit includes a grid resistor 64 and a source 65 for applying a constant cut-off bias. The plate circuit of tube 63 is energized through a transformer 68 by alternating-current 1 voltage drop occurring across the tapped portion of rheostat 89 when the tube 63 is conductive are cumulatively imposed on the grid circuit of a tube 18 preferably of the thyratron type. The .grid

circuit of tube I0 can be traced from grid II to a resistor 12, a source 13 of a constant bias voltage, the tap portion of rheostat 5, contact 80, and the tapped portion of rheostat 69 to the cathode of tube I0. The plate circuit of tube 10 includes the coil 14 of a control relay R2 and is energized from direct-current terminals 15 and 16 under control by the contact 51 of the eontactor C4. The system includes further an operator-actuable switch whose two contacts 18 and 19 are to be closed by a push button or the like actuating member in order to start the motor MI and which has also a push button or the like member 8| to be actuated for stopping the motor MI. The performance of this system is as follows: I

It is assumed in the following that the running generator GR is operating and that the motor M4 is running at the desired speed determined by the selected field excitation of generator GR. In order to start the motor M3, the actuating member 80 is depressed by the operator so that contacts I8 and 19 close. These contacts stay closed during the subsequent performance until the mgmber 8| is actuated in order to stop the motor M circuit of coil 52 so that contactor C3 picls up and closes at contact 5| the starting connections for motor Ml. At this moment the voltage of the generator GS is zero so that the voltage drop between points P5 and P6 of rheostat 6| corresponds to the full line voltage then effective. As a result, the normal blocking bias of source 65 is overcome and the tube 63 is triggered immediately or is raised to such a degree of conductance that a substantial voltage drop appears across the rheostat 63. This voltage drop imposes a negative cut-off bias on grid H of tube I0 which preponderates over the normal positive bias from source 13 and hence holds the tube I0 safely under non-conductive conditions. The starting generator GS is now caused to furnish an increasing starting voltage, so that the motor M3 accelerates. The accelerating current causes a corresponding voltage drop to be efiect-ive across points P4 and P5 of rheostat 54, and this voltage drop has also the effect of overcoming-the normal bias from source 13 in the grid'circuit of tube 10. As the voltage of the starting generator GS approaches the normal voltage range of the running generator GR, 3. point-will be reached where the voltage drop across pointsP5 and P6 of rheostat 6| becomes insuihcient to maintain the tube 63 sufliciently conductive. Then, the voltage drop across the tapped portion of rheostat 69 disappears or is reduced sufficiently to render the firing bias of source 13 effective. long as the motor is still accelerating, the voltage drop across points P4 and P5 of rheostat 54 will still prevent the tube 10 from firing. With the motor M l running at the properly matched speed, the conditions in the grid circuit of tube 10 are such as to trigger the tube. Then the relay R2 picks up and, by closing the contact 11, energizes The closing of contact 19 completes the However, as

7 the coil 56 of contactor 04. Contact 55 closes and completes the permanent running connections fan motor Ml while interlock contact 59 opens the coil circuit of contactor C3, so that the latter drops out. At that time, however, a selfholding circuit is closed for contactor C4 at contact 58. The contacts 51 and 60 interrupt the plate and grid circuits, respectively, of the tube so that the performance of this tube is limited to a rather brief interval of operation. The subsequent actuation of button 8| has the effect of opening the contact 18 of the coil circuit for contactor 04 so that the latter will drop out and stop the motor M3. Thereafter the system is again in the initial condition illustrated in the drawings.

It will be understood by those skilled in the art that control systems according to the invention can be modified and altered in many respects, especially as regards the individual components of the control system and their mutual connections without departing from the above disclosed principles of my invention and within the scope of its essential features as set forth in the claims annexed thereto.

I claim as my invention:

1. A system for transferring a direct-current motor from starting to running connections, comprising voltage-responsive control means responsive to the occurrence of a given low differential voltage between running and starting connections, current-responsive control means responsive to the occurrence of a given'low motor current, electromagnetic contactor means having contacts for switching the motor from starting to running connections and coil means for controlling said contacts, an electronic trigger tube having a plate circuit connected with said coil means and having a trigger circuit connected with said voltage-responsive control means and said current-responsive control means fortriggering said tube only when both said control means have responded to said given voltage and current respectively.

2. A direct-current bus-transfer system, comprising a motor circuit, starting connections and running connections for energizing said motor circuit, electromagnetic contactor means disposed between said circuit and said connections and having coil means for switching said circuit from said starting connections to said running connections, a circuit member connected between said starting connections and said running connections to provide a first control voltage in accordance with the voltage diiference of said respective connections, control means connected to said member so as to change its condition when said first control voltage drops below a given magnitude, another circuit member connected to said motor circuit for providing a second control voltage in accordance with the current in said motor circuit, an electronic trigger tube controlled by said control means and having a plate circuit connected to said coil means and a trigger circuit connected with said other member so as to be triggered only when said first control voltage is below said given value and said second control voltageis also below 'a given value.

3. A direct-current bus-transfer system, comprising a motor circuit, starting connection and running connections for energizing said motor circuit, electromagnetic contactor means for switching said motor circuit from said starting connections to said running connections, an electromagnetic relay having contacts connected to said con-tactor means for controlling the latter 8 and having a coil for actuating said contacts, an electronic tube plate-connected'to said coil for providing energization for the latter, circuit means attached to said tube for controlling said energization and including two control means of which one is connected between said respective starting connections and running connections to respond to the diflerential voltage of said respec tive connections, while said other control means is connected to said motor circuit under control by saidcontactor means when said motor circuit is connected to said starting connections in order to respond to the current then flowing in said motor circuit so that said tube causes said relay to actuate said contactor means for switching said circuit from starting to running connections when said differential voltage and said current are both below given respective magnitudes.

4. A direct-current bus-transfer system, comprising a motor circuit, starting connections and running connections for energizing said motor circuit, electromagnetic contactor means for switching said mot-or circuit from said starting connections to said running connections, an electromagnetic relay having contacts connected to said contactor means for controlling the latter and having a coil for actuating said contacts, an electronic tube plate connected to said coil for providing energization for the latter and having a grid circuit for controlling said energization, two impedance devices connected in said grid circuit for impressing thereon two respective component control voltages, one of said impedance devices being connected between said starting connections and said running connections respectively as to furnish one of said control voltages in accordance with the voltage differential of said respective connections, said other impedance device being connected in said motor circuit to furnish said other control voltage in dependence upon the current flowing in said motor circuit when the latter is connected to said starting connections, said two impedance devices having a polarity of connection relative to each other in said grid circuit as is required to make said control voltages cumulative so that said tube causes said relay to effect switching of said motor circuit by said contactor means only when said voltage differential and said current are both below predetermined respective magnitudes.

5. A direct-current bus-transfer system, comprising a motor, a common bus connected to said motor, a starting bus and a running bus selective- 1y connectible to said motor, a first electromagnetic con'tactor for connecting said motor to said starting bus, a second electromagnetic contactor for connecting said motor to said running bus, such of said contac-tors having a coil circuit controlled by the other contactor to provide a mutual interlock between said contactors, an electromagnetic relay having a normally closed first contact in said coil circuit of said first con-tactor and a normally open second contact in said coil circuit of said second contactor and having a coil for controlling said contacts, a control contact disposed in said coil circuit of said first contactor to permit closing said firs-t contactor when said first contact is closed, an electronic tube having a plate circuit connected to said relay coil for causing it, when energized, to open said first contactor and closing said second contactor, and circuit means connected to said tube for controlling the latter and including two control means, one of said control means being connected across said respective starting and running buses to respond .to the differential voltage of said latter buses, and said other control means being connected to said motor to respond to the current flowing through said motor when said motor is connected to said starting bus, said two control means being disposed in said circuit means for conjoint control of said tube so that said tube causes said relay to respond only when said diiierential voltage and said current are both below predetermined respective magnitudes.

6. A direct-current bus-transfer system, comprising a motor, a common bus connected to said motor, a starting bus and a running bus selectively connectible to said motor, a first electromagnetic contactor for connecting said motor to said starting bus, a second electromagnetic contactor for connecting said motor to said running bus, each of said contactors having a coil circuit controlled by the other contactor to provide a mutual interlock between said contactors, an electromagnetic relay having a normally closed first contact in said coil circuit of said first contactor and a normally open second contact in said coil circuit of said second contactor and having a coil for controlling said contacts, a control contact disposed in said coil circuit of said first contactor to permit closing said first contactor when said first contact is closed, an electronic tube having a plate circuit connected to said relay coil for causing it, when energized, to open said first contactor and closing said second contactor, said tube having agrid circuit provided with two resistors, one of said resistors being connected between said start? ing busand said running bus so as to impress on said grid circuit a component grid voltage proportional to the voltage difference of said latter buses, and said other resistor being connected to said motor so as to impress on said grid circuit another component grid voltage determined by the load current flowing through said motor, said two resistors being interconnected to make said two component grid voltages cumulative so that said tube causes said relay to switch said contactors only when said voltage differential and said currert are below predetermined respective magnitu es.

7. In combination with a bus-transfer systemas set forth in claim 6, an auxiliary electromagnetic relay having a coil connected across said starting bus and said running bus so as to be picked up when said voltage diflerential is high and being rated to drop out when said voltage differential drop below a given magnitude higher than the aforesaid predetermined magnitude, said auxiliary relay having a contact disposed in said plate circuit for interrupting the latter circuit when said auxiliary relay is in picked-up condition.

8. In combination with a bus-transfer system as set forth in claim 6, an auxiliary electromagnetic relay having a coil connected across said starting bus and said running bus so as to be picked up when said voltage difierential is high and being rated to drop out when said voltage differential drop below a given magnitude higher than the aforesaid predetermined magnitude, said auxiliary relay having a contact disposed in said plate circuit for interrupting the latter circuit when said auxiliary relay is in picked-up condition, another contact connected with said one resistor for opening its connection between said starting bus and running bus as long as said auxiliary relay is in picked-up condition, and a third contact for disconnecting said grid circuit from said other resistor when said auxiliary relay is in picked-up condition.

9. A direct-current bus-transfer system, comprising a motor circuit, starting connections and running connections for energizing said motor circuit, electromagnetic oontactor means for switching said motor circuit from said starting connections to said running connections, an electromagnetic relay having contacts connected to said contactor means for controlling the latter and having a coil for actuating said contacts, an electronic tube plate connected to said coil for providing energization for the latter and having a grid circuit tor-controlling said energization, two impedance devices connected in said grid circuit for impressing thereon two cumulative control voltages, one of said impedance devices being connected between said starting connections and running connections respectively as to furnish one of said control voltages in accordance with the voltage differential of said respective connections, said other impedance device being connected in said motor circuit to furnish said other control voltage in dependence upon the current flowing in said motor circuit when the latter is connected to said starting connections, and auxiliary relay means connected between said starting and running connections respectively and rated to perform responsive action when said voltage differential drops below a given magnitude, said relay means being connected to said v tube so as to put said tube in operative condition only upon occurrence of said responsive action, and said two impedance devices being interconnected and rated so as to thereafter cause said tube to energize said relay to efiect switching of said motor circuit only when said voltage differential drops below a predetermined value lower than said magnitude while said current is below a given load magnitude.

EARL B. ANKENMAN.

REFERENCES CITED UNITED STATES PATENTS Name Date Sloane M r. 7, 1939 Number 

